The narrator of James Hynes’s novel is an orphaned slave boy who does not know his age, his origins or even his name. He lives in the crumbling city of Carthago Nova (now Cartagena in Spain) during the last days of the Roman empire. His world is confined to his place of forced labour, which is “a cramped, smoky kitchen and a narrow garden ten paces across”.

The kitchen is part of Helicon, a brothel and tavern. Here, the boy sleeps in a corner “among the cockroaches and mouse pellets”. He is fascinated by birds and so calls himself Sparrow, a name that allows him to enter an imaginative world where he can forget his fear and pain and fly high above the confines of his troubled existence.

Sparrow’s only friend is Euterpe, one of the “wolves” (prostitutes). Euterpe tries to educate and care for Sparrow, but in the world of Helicon there is no place for kindness. The fear of death is ever-present and Euterpe has no power against the brothel manager, Audo. Sparrow tells us that “Audo is a hammer and every problem is a nail”.

As the inhabitants of Carthago Nova turn to Christianity, the brothel starts to lose money and Audo becomes aware that Sparrow is “a pretty boy”. “Reader, I know you know where this is going,” says Sparrow. The reader does indeed know. Sparrow, though still a child, soon comes to know the “smack of a cock being sucked”.

When one of the wolves, Melpomene, takes over the running of the brothel, there is hope that things might change. But for Melpomene “the whole world is a whorehouse” and she presses the other wolves to work even harder. Earning more tips is the only route to freedom.

Euterpe and Sparrow finally decide to attempt an escape. But from the beginning of the book, Sparrow has told the reader that no happy ending is possible. “No touching final reunion will ever be performed in this play. Nothing will be revealed, or redeemed or healed. The story will simply stop.”

There is some wonderful writing in this novel. Sparrow’s voice is original and moving and the gruelling work of the brothel becomes absolutely real. The wolves and their shifting relationships – by turns tender, competitive and bullying – are beautifully portrayed. Yet ultimately this book does not entirely succeed.

It is too long and the real action of the story does not start until halfway through. Also, the cruelty is relentless. A kitchen table abortion. Rape, beatings, murder. Runaway slaves with iron collars round their necks, slaves with their tongues cut out. All this is, of course, historically accurate.

But the details of brothel life come to seem gratuitous and the reader is cast in the uncomfortable role of voyeur. Usually, a writer uses foreshadowing techniques to keep the reader interested and to hint that some resolution is coming. Here, foreshadowing is used to kill any expectation of either resolution or meaning.

Of course, a novel does not need to redeem or heal. But the reader does expect to see some aspect of human life in a new light. Here it is certainly demonstrated that the Roman empire “is a mosaic of rape and murder and bastardy and forced labour”. But the problem is that this is not new. In the prologue, Sparrow says: “This is just another book which changes nothing.” It would have been interesting to get more of a sense of what Hynes wanted the reader to take away from this brutal story.

• Sparrow by James Hynes is published by Picador (£16.99). To support the Guardian and Observer, order your copy at guardianbookshop.com. Delivery charges may apply.